``It was nervous today, but quite easy,'' the three-time defending champion said.
Armstrong finished the second stage in 61st place, and slipped to fourth in the overall standings. He isn't expected to bid for the lead until the race reaches the mountains next week.
Oscar Freire of Spain won the 112.2-mile trek, sprinting over the line just ahead of the main pack that included Armstrong. Swiss rider Rubens Bertogliati retained the leader's yellow jersey he took from Armstrong on Sunday.
The Texan is taking the early, flat stages easy. But for some, even Monday's ride was nearly too much.
Norway's Thor Hushovd shared the lead for much of the day but finished last after stopping several times with cramps. At one point, he hunched over his handlebars in pain and had to have his thigh massaged by a trainer. He was cheered on by fans as he struggled to the finish line.
``I was surprised by the huge crowds - I was impressed,'' said Armstrong, who is favored to win a fourth straight title.
Thousands lined the stage route between Luxembourg and this west German city to cheer him and other riders, particularly Erik Zabel. One woman had ``Zabel'' written on her belly in the pink colors of his Telekom team.
But Freire, the world road champion, spoiled the party by outflanking the German in the final few yards to win in 4 hours, 19 minutes, 51 seconds. Australia's Robbie McEwen placed second and Zabel finished third, in the same time as Freire. The main pack also had the same time.
Zabel, who turned 32 on Sunday, was wearing the green jersey awarded to the Tour's fastest sprinter as he entered Saarbruecken.
``To return to my country in the green jersey, it's still not too bad,'' he told France-2 Television.
Freire said riders can't always win on their home turf.
``In cycling, when you arrive in your home country, you indeed have more desire to win,'' Freire said. ``But the other rivals also want to win - we're all racing out there to win.''
There were four crashes in Monday's stage. One of them involved Armstrong's U.S. Postal Service teammate Benoit Joachim, who wasn't seriously hurt. Spain's Samuel Sanchez of Euskaltel was taken to a hospital in Saarbruecken for X-rays after injuring his right knee and right elbow in the second crash.
Bertogliati said he hadn't expected to retain the lead.
``Today, I had a bit of luck to retain the yellow jersey for a second day,'' Bertogliati said. ``If I hold it again after tomorrow's stage, I'm going to go buy a lottery ticket.''
The riders were to move into France for Tuesday's third stage, a 108.19-mile run from Metz to Reims, the capital of the Champagne region.
Stage 2: Post-stage commentary
Stage 2: Live update summary
Stage 2 results, top 15
Luxembourg to Saarbrucken (181 km)
1. Oscar Freire (Spa/MAP) 181km in 4hr 19 min 51sec (average: 41.793 kph)
2. Robbie McEwen (Aus/LOT) at 00:00
3. Erik Zabel (Ger/TEL) 00:00
4. Baden Cooke (Aus/FDJ) 00:00
5. Jaan Kirsipuu (Est/A2R) 00:00
6. Andrej Hauptman (Slo/TAC) 00:00
7. Pedro Horillo (Spa/MAP) 00:00
8. Fred Rodriguez (USA/DFF) 00:00
9. Gian Matteo Fagnini (Ita/TEL) 00:00
10. Stuart O'Grady (Aus/C.A) 00:00
11. Danilo Hondo (Ger/TEL) 00:00
12. Jan Svorada (Cze/LAM) 00:00
13. Francois Simon (Fra/BJR) 00:00
14. Paolo Bossoni (Ita/TAC) 00:00
15. Nico Mattan (Bel/COF) 00:00
Overall standings after Stage 2 (top 10)
1. Rubens Bertogliati (Swi/LAM) 9hr 18min 12sec.
2. Erik Zabel (Ger/TEL) at 00:02.
3. Laurent Jalabert (Fra/CST) 00:03.
4. Lance Armstrong (USA/USP) 00:03.
5. Raimondas Rumsas (Lit/LAM) 00:06.
6. Santiago Botero (Col/KEL) 00:07.
7. David Millar (Gbr/COF) 00:08.
8. Laurent Brochard (Fra/DEL) 00:09.
9. Oscar Freire (Spa/MAP) 00:11.
10. Dario Frigo (Ita/TAC) 00:11.